NEWPORT NEWS, va. — As the Obama administration weans the U.S. off dirty fuels blamed for global warming, energy companies have been sending more of America’s unwanted energy leftovers to other parts of the world.

This fossil fuel trade threatens to undermine President Barack Obama’s strategy for reducing the gases blamed for climate change. The contribution of this exported pollution to global warming is not something the administration wants to measure, or even talk about.

“This is the single biggest flaw in U.S. climate policy,” said Roger Martella, the former general counsel at the Environmental Protection Agency under President George W. Bush. “Although the administration is moving forward with climate change regulations at home, we don’t consider how policy decisions in the United States impact greenhouse gas emissions in other parts of the world.”

Over the past six years, American energy companies have sent more coal than ever before to other parts of the world, in some cases to places with more lax environmental standards.

The consequence: This global shell game makes the U.S. appear to be making more progress than it is on global warming. That’s because it shifts some pollution — and the burden for cleaning it up — onto other countries’ balance sheets.

“Energy exports bit by bit are chipping away at gains we are making on carbon dioxide domestically,” said Shakeb Afsah, an economist who runs an energy consulting firm in Bethesda, Md.

As companies look to double coal exports, with three new terminals on the West Coast, America could be fueling demand for coal when many experts say that most fossil fuels should remain buried to avert the worst effects of climate change.

But the administration has resisted calls from governors in Washington and Oregon to evaluate and disclose such global fallout.

White House officials say U.S. coal has a negligible global footprint and reducing coal’s use worldwide is the best way to ease global warming. The U.S. in 2012 accounted for 9 percent of worldwide coal exports, the latest data available.

“There may be a very marginal increase in coal exports caused by our climate policies,” said Rick Duke, Obama’s deputy climate adviser. “Given that coal supply is widely available from many sources, our time is better spent working on leading toward a global commitment to cut carbon pollution on the demand side.”

Guidance drafted by the White House in 2010 did outline how broadly agencies should look at carbon emissions from U.S. projects. Four years later, that guidance is still under review.

“They have sat on their hands,” said George Kimbrell, a senior attorney for the Center for Food Safety, which has sued the administration over the delay.

Changing the global system to account for production would carry political risks, especially for the U.S., which is trying to boost production of energy and exports even as it addresses global warming.

“The U.S. needs to be pragmatic on this,” said Jason Bordoff, director of Columbia University’s Center on Global Energy Policy. “If our coal exports are very small and having no or little impact on global greenhouse gas emissions … the government has to take into account the economic and foreign policy costs of restricting exports.”

He was a National Security Council energy and climate change adviser to Obama until January 2013.

Over the past six years, as the U.S. cut coal consumption by 195 million tons, about 20 percent of that coal was shipped overseas, according to an AP analysis of Energy Department data.

Less coal being burned here has helped the power sector reduce carbon emissions by 12 percent and left more coal in the ground. But a growing share is finding its way abroad.

U.S. exports to Germany have more than doubled since 2008. German environmental officials say the recent boom in coal-fired power is making it harder for the country to meet its climate-protection goals, even as it has increased renewable energy and participates in a carbon market that has lowered emissions throughout Europe.